People with colorectal cancer that cannot be cured by surgery are being asked to participate in this study.

The purpose of this study is to test the efficacy (effectiveness) of a new combination of drugs, ABT-888 and temozolomide for patients with colorectal cancer. Temozolomide acts by damaging deoxyribonucleic acid (DNA) in rapidly dividing cells, in other words, cancer cells. ABT-888 inhibits an enzyme called "PARP" which helps to fix damaged DNA. By inhibiting this enzyme, ABT-888 prevents cancer cells from repairing the damage caused by the temozolomide, and will hopefully increase the killing of cancer cells, and decrease the tumors in the body.

ABT-888 is an investigational or experimental anti-cancer agent that has not yet been approved by the Food and Drug Administration (FDA) for use in colorectal cancer.

This study will help find out what effects (good and bad) the combination of drugs, temozolomide and ABT-888 has on colorectal cancer.

This research is being done because it is not known if ABT-888 will increase the effectiveness of temozolomide for colorectal cancer.

We will initiate a single arm, open label Phase II study to test the clinical activity of ABT-888 and temozolomide in patients with metastatic colorectal cancer.

Treatment will continue weekly with restaging scans to be performed every 8 weeks. The trial will follow a Simon's two-stage optimal design. For the first stage, 21 patients will be accrued. If two (9.5%) or fewer of the 21 patients exhibit a partial or complete response with ABT-888 plus temozolomide, the agent will be rejected and the trial stopped. However, if at least 3 patients of the 21 (14%) exhibit a response in the first stage, then an additional 29 patients will be entered into the second stage, for a total of 50 patients in this phase II study. If 8 (16%) or more patients exhibit a response, then the treatment will be considered for further investigation. The sample sizes of 21 and 50 patients and the decision rules, in stages 1 and 2 respectively, are designed to differentiate a 25% overall response rate from a 10% overall response rate.

Inclusion Criteria:

• Histologically proven colorectal cancer with measurable or evaluable disease
• Progression on or intolerance of or ineligibility for all standard therapies (including regimens containing fluoropyrimidine, oxaliplatin, irinotecan, bevacizumab, and an anti-EGFR antibody (where appropriate))
• Age > = 18 years
• ECOG performance status 0-2
• Subjects with no brain metastases or a history of previously treated brain metastases who have been treated by surgery or stereotactic radiosurgery at least 4 weeks prior to enrollment and have a baseline MRI that shows no evidence of active intercranial disease and have not had treatment with steroids within 1 week of study enrollment
• At least 21 days since prior anti-cancer therapy, including chemotherapy, biological therapy, radiation therapy or any investigational agent within 4 weeks before starting ABT-888 and temozolomide
• Adequate hepatic, bone marrow, and renal function
• Partial thromboplastin time (PTT) must be </= 1.5 x the upper limit of institution's normal range and INR < 1.5. Subjects on anticoagulant will have PTT and INR as determined by the investigator.
• Subject's with significant fluid retention, including ascites or pleural effusion, may be allowed at the discretion of the PI
• Life expectancy > 12 weeks
• Women of childbearing potential must have a negative serum pregnancy test within 14 days prior to initiation of treatment and/or postmenopausal women must be amenorrheic for at least 12 months to be considered of non-childbearing potential.
• Subject is capable of understanding and complying with parameters as outlined in the protocol and able to sign and date the informed consent approved by the IRB prior to the initiation of any screening or study-specific procedures.

Exclusion Criteria:

• CNS metastases which do not meet the criteria outlined in inclusion criteria
• Active severe infection or known chronic infection with HIV, hepatitis B virus, or hepatitis C virus
• Cardiovascular disease problems including unstable angina, therapy for life-threatening ventricular arrhythmia, myocardial infarction, stroke or congestive heart failure within the last 6 months
• Life threatening visceral disease or other severe concurrent disease
• Women who are pregnant or breastfeeding
• Anticipated patient survival under 3 months
• The subject has had another active malignancy within the past five years except for cervical cancer in site, in situ carcinoma of the bladder or non-melanoma carcinoma of the skin.
• Clinically significant and uncontrolled major medical conditions including but not limited to: active uncontrolled infection, symptomatic congestive heart failure, Unstable angina pectoris or cardiac arrhythmia, psychiatric illness/ social situation that would limit compliance with study requirements; any medical condition, which in the opinion of the study investigator places the subject at an unacceptably high risk for toxicities